This invention relates, in general, to a method for removing nitride coatings from metal surfaces, and more particularly to a method of removing nitride coatings from metal surfaces employing a gaseous plasma comprising a reactive fluorine species.
Metal tooling and mold surfaces are commonly coated for protection, to improve the wear characteristics and to better interact with the materials that the metal surface comes in contact with. Metal tooling and mold surfaces commonly employ chromium coatings for these reasons. However, once the chromium coating starts to wear through, it is extremely difficult to remove so that the metal tooling and mold surfaces may be recoated. One method of removing chromium coatings is reverse plating. However, this will often damage the underlying base metal, especially if the underlying base metal contains chromium itself. Another method used for removing chromium coatings is a wet chemical etch. Wet chemical etches often do not etch uniformly and therefore, the etch may also damage the underlying base metal. When the underlying base metal is damaged, the metal tooling or mold surface often will need to be reworked or will be rendered non-usable.
Another coating commonly used with metal tooling and molds is titanium nitride. In addition to improving wear characteristics and increasing metal tooling or mold lifetime, titanium nitride has excellent lubricity and is excellent n conjunction with plastics. However, titanium nitride is also difficult to remove from metal tooling and mold surfaces without damaging the underlying base metal. Various removal methods include wet chemical etching which encounters the same problems with titanium nitride as discussed above with chromium. Also employed is media blast removal. Again, this results in an uneven removal of the titanium nitride and possible damage to the underlying base metal.
Therefore, it would be highly desirable to have a method to remove coatings from metal tooling and mold surfaces that does not damage the underlying base metal.